By Dominic Reisig
I call the first week of September looper week. Soybean loopers cannot overwinter in North Carolina and migrate yearly from the south. The adults show up in late August and lay eggs that develop into larvae that feed on soybean leaves in early September. This 2023 article details their biology, why they are frustrating to control, and some insecticide recommendations.
Here is an updated table of efficacy. More consistently effective options include Blackhawk, Denim, Intrepid Edge, and Steward.
Soybean loopers tend to be more common in coastal counties. However, they can occur well into the Coastal Plain and even the Piedmont.
Yield loss from leaf feeding can occur into R6 (full seed), and numbers will vary from field to field. Be sure to check any soybeans that are still forming pods or filling seeds. Looper larvae prefer older leaves and will be in the bottom of the canopy, so be sure to inspect the canopy thoroughly.
Source : ncsu.edu